Power semiconductor devices and integrated circuits processed on a common semiconductor substrate or wafer are separated by sawing or laser cutting of the wafer. Commonly, no additional passivation is provided on the separation edge formed by sawing or laser cutting, and the separation edges are merely covered by the moulding used for forming the device housing. Along the formed separation edges, crystal distortion and unsaturated bonds may remain which can act as generation centres particularly when the semiconductor device is subjected to high temperatures, humidity and varying temperature conditions.
Under high reverse or blocking voltages applied to the semiconductor device, electron-hole pairs may be generated at the generation centres. In case of an n-channel power-FET with a positive voltage applied between drain and source, the electrons can freely drift from the weakly n-doped drift region to the highly n-doped drain region and the drain electrode. On the other hand, the holes may reach the p-doped body region and eventually causes a leakage current. Furthermore, electrical conductors or a humid moulding arranged next to a silicon-oxide interface, which is usually arranged at the principal surface and formed, for example, by field oxides, may cause generation of a hole-inversion channel between the separation edge and a body region, which is electrically connected to source, if the electrical conductors or the humid moulding have an electrical potential which is less than the electrical potential of drain or which is close to the electrical potential of source. Further, p-doped regions and metallic regions arranged close to the separation edges may also contribute to the hole current.
For terminating the semiconductor device at its periphery, field plates are commonly used which are arranged on, and insulated from, the semiconductor substrate. The field plates are connected to a body region and/or source region on high potential to suppress any channel formation in the termination region. Another approach uses channel stop trenches for suppressing the channel in the termination region of the semiconductor device.
For these and other reasons, there is a need for the present invention.